1. Field of the Invention:
This invention relates to a pressure-sensitive element which may, for example, be used for detecting the taking of a seat in an airplane or automobile, or for composing an X-Y coordinate input device. More particularly, it is concerned with a sheet material used for making a pressure-sensitive element.
2. Description of the Prior Art:
A known pressure-sensitive element contains electrically conductive particles in an electrically insulating elastic material, such as rubber. If the element is compressed, the conductive particles contact one another to form a path for electric conduction. The removal of the pressure disconnects the particles from one another and brings the element back to its electrically insulated condition. The element usually has a resistance of at least 10.sup.7 .OMEGA. cm when it is in its insulated condition, and a resistance not exceeding 10.sup.3 .OMEGA. cm when it is in its conductive condition. This resistance depends on the degree to which the particles approach or contact one another when pressure is applied to the element. The element has, therefore, the disadvantage of having its electrical conductivity depending largely on the pressure applied thereto and being, therefore, unsatisfactory in the reliability and stability of operation.
There is known an X-Y coordinate input device which is called a matrix sheet, and which comprises a pair of substrates formed each with a multiplicity of thin electrodes lying in parallel to one another, and facing each other so that the electrodes on one of the substrates may extend in the X direction, while the electrodes on the other substrate extend in the Y direction which is perpendicular to the X direction, and a pressure-sensitive electrically conductive sheet disposed between the substrates. The electrodes on each substrate are formed by the etching of copper foil bonded thereto. It is necessary for the electrodes to be thin and close to one another in order to improve the dissolution of the device. This requirement gives rise to the breakage of electrodes during their formation by etching and the contact of two or more adjoining electrodes.
There is also known a matrix sheet which comprises a sheet woven from electric wires each covered by an insulating film which is partly removed mechanically as by sandpaper. The mechanical removal of the insulating film is, however, difficult to achieve uniformly. Moreover, it is likely to do damage to the wire surfaces or cause the displacement of the wires.